1. Field of the Invention
Embodiments of the present invention relate generally to optical communication systems and components and, more particularly, to a liquid crystal-based optical device that is configured to reduce polarization dependent loss and polarization mode dispersion.
2. Description of the Related Art
In optical communication systems, it is sometimes necessary to perform 1×2 switching of an optical signal, where an input light beam enters an optical switching device through an input port and is directed to one of two output ports. There are also more complicated optical switching schemes, such as 2×2, 1×N, and N×N optical switches, which may be realized by combining multiple 1×2 optical switches.
In addition to routing of signals by optical switches, attenuation of signals in optical communication systems is needed, for example in an optical communication system that employs wavelength division multiplexing (WDM). In such an optical system, information is carried by multiple channels, each channel having a unique wavelength. WDM allows transmission of data from different sources over the same fiber optic link simultaneously, since each data source is assigned a dedicated channel. The result is an optical communication link with an aggregate bandwidth that increases with the number of wavelengths, or channels, incorporated into the WDM signal. In this way, WDM technology maximizes the use of an available fiber optic infrastructure, such that what would normally require multiple optic links or fibers instead requires only one. In practice, different wavelength channels of a WDM signal typically undergo asymmetrical losses as they travel through an optical communication system, resulting in unequal intensities for each channel. Because these unequal intensities can compromise the integrity of the information carried by the WDM signal, an optical device or array of optical devices is used in WDM systems to perform attenuation to equalize the respective intensities of the channels contained in a WDM signal.
Liquid crystal (LC) based optical switches are known in the art for switching and attenuation of the channels contained in a WDM signal. An LC-based optical switch relies on rotating the polarization state of linearly polarized input beam to perform switching and attenuation functions. The LC-based optical switch divides an input beam into s- and p-polarized components, and manages the switching and attenuation of each component separately. The division of the input beam into s- and p-polarized components produces two negative effects that need to be compensated. The first is polarization dependent loss (PDL). The s- and p-polarized components experience different losses as they pass through various elements of the LC-based optical switch. The second is polarization mode dispersion (PMD). PMD occurs because of random imperfections and asymmetries in the optical medium that is traversed by the s- and p-polarized components. For optimal performance of the LC-based optical switch, the PDL and the PMD need to be minimized.